The biggest difference is that Optifast is a medically supervised weight loss program. In addition to the restricted-calorie mostly liquid diet with Optifast you will have usually weekly consultations with a doctor or counselor. Also Optifast has a re-introduction phase to the program to try to teach you how to introduce real food back into your routine. Optifast is normally only available through an authorized clinic, although I know that you can buy some of the products over the internet, whereas Medifast is available without going to a clinic. Both programs have been successful for people able to stick to the severe restrictions, so it is pretty much up to you whether you prefer a program with assistance and counseling or if you feel more comfortable doing it privately.

I have a friend who lost a lot of weight with Medifast Meal Replacement program. It is all about portion control.

There is an article here that highlights both MediFast and the Optifast programs, as well as South Beach Diet.
http://www.secretprices.com/choose-a-die...